Test suite: Fix typo in test name
cxxll::rpm_file_entry: Move class into its own header file
cxxll::rpm_parser: Renamed from class cxxll::rpm_parser_state
cxxll::const_stringref: Move noreturn attribute to the right place
cxxll::call_throw: New function template
cxxll::pg_split_statement: Use cxxll::call_throw
cxxll::database: Use throw to throw exceptions
cxxll::call_throw: Add std::string overload
cxxll::raise: Rename from cxxll::call_throw
cxxll/raise.hpp: Rename from cxxll/exception.hpp
Split up lib/cxxll/os.cpp

Move all implementation files to their own directory.
Use cxxll::raise throughout the code base

This reduces executable sizes by about 1%.